This application is based upon and claims the benefit of Japanese Patent Applications No. 2000-282256 filed on Sep. 18, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a method for manufacturing a sensor apparatus including a sensor element that is disposed in a recess formed in a case for measuring an external environment of the recess.
2. Description of the Related Art
An atmospheric pressure sensor for detecting an atmospheric pressure is known as this kind of sensor apparatus. FIG. 1 shows a structure of an atmospheric pressure sensor J1. In the sensor J1, leads are insert-molded in a case 1, and a recess 2 is formed in the case 1. A sensor chip is disposed in the recess 2 as a pressure detecting element for detecting an atmospheric pressure outside the recess 2. The sensor chip 3 is electrically connected to the leads 6 through wires 7.
Gel 8 is disposed on the surface of the sensor chip 3 for protecting the sensor chip 3. A lid 200 is bonded to the case 1 by adhesive or the like to close the opening portion of the recess 2. The lid 200 has a hole 201 through which inside and outside of the recess 2 communicate with each other, and the atmosphere is introduced into the recess 2 through the hole 201 so that the sensor chip 3 detects the atmospheric pressure. The atmospheric pressure sensor J1 is attached to a member (not shown) such as a printed board, and the leads 6 are electrically connected to the member, thereby constituting a sensor apparatus.
Next, a method for manufacturing the sensor apparatus is explained referring to FIGS. 2A to 2D and 3A to 3C.
First, as shown in FIG. 2A, the atmospheric pressure sensor J1 shown in FIG. 1 is prepared, and as shown in FIG.2B, a masking tape 202 is adhered to the lid 200. Then, referring to FIG. 2C, the sensor J1 is mounted on a printed board 20 through cream solder 21. As shown in FIG. 2D, the solder 21 is reflowed by hot air (as indicated by arrows Y1 in FIG. 2D), so that the leads 6 are electrically connected to the printed board 20, and the atmospheric pressure sensor J1 and the printed board 20 are integrally bonded to each other.
After that, referring to FIG. 3A, the integrated sensor J1 and the board 20 are immersed into washing solution 22 to remove solder flux, and then are dried. Next, damp proof agent is applied to the entire surface of the atmospheric pressure sensor J1 and the printed board 20 by, for example, splaying it in a direction indicated by arrows Y1 in FIG. 3B.
After the damp proof agent is dried, the masking tape 202 is peeled off as shown in FIG. 3C. Thus, the sensor apparatus having the atmospheric pressure sensor J1 mounted on the printed board 20 is completed. The sensor apparatus is shipped after undergoing various tests. The sensor apparatus is installed in, for example, a vehicle ECU as an atmospheric pressure sensor for adjusting atmospheric pressure in a system such as an automotive EFI (Electronic Fuel Injection system).
Here, the reason why the masking tape 202 is used in the above-described method is as follows.
If the washing solution 22 intrudes the recess 2 through the hole 201 of the lid 200 without the masking tape 202, the washing solution 22 may adversely affect sensor characteristics by swelling not only the gel 8 for protecting the sensor chip 3 but also the adhesive 5 adhering the sensor chip 3 to the case 3.
Likewise when the damp proof agent intrude the recess 2, the gel 8 and the adhesive 5 maybe swelled due to a diluted component of the damp proof agent, and the wires 7 may be broken due to stress produced when the damp proof agent is hardened. Thus, the intruding damp proof agent would adversely affect the sensor characteristics and the structure. Therefore, the masking tape 202 is used to prevent the washing solution 22, the damp proof agent and other foreign matters from intruding the recess 2. However, because the masking tape 202 must be detached after the damp proof agent is dried, the number of manufacturing steps is increased.
The present invention has been made in view of the above problems. An object of the present invention is to provide a simplified method for manufacturing a sensor apparatus including a sensor element disposed in a recess of a case for detecting an external environment of the recess.
According to the present invention, in a method for manufacturing a sensor apparatus, after a sensor element is disposed in a recess of a case, an opening portion of the recess is closed with a sheet member. After that, a through hole is formed in the sheet member so that an inside and an outside of the recess communicate with each other through the through hole.
Accordingly, when washing or application of damp proof agent is performed after the opening portion of the recess is closed with the sheet member and before the through hole is formed in the sheet member, the sheet member can prevent foreign matters from intruding inside the recess. The sheet member needs not be detached after such treatment. As a result, the method for manufacturing the sensor apparatus is simplified.